After grid-connected microgrid entry into islanded operation mode

the reliability in its future short-term run is variable with time. A reliability evaluation method based on the time-varying universal generating function (TVUGF) is proposed. The state probabilities of forecast wind and time-varying state probabilities of microgrid system are obtained based on Markov-TVUGF model. And TVUGF models of distributed generator output power are obtained as well. Further

the classified fault impact is analyzed for each system state

to develop the microgrid reliability TVUGF model. And microgrid load points and system reliability indices are obtained. With planned microgrid splitting and island load shedding strategy taken into account

the microgrid reliability model based on TVUGF is developed. And

in consideration of the large number of states to be calculated in TVUGF operation

the method of merger of similar items and re-division of states is proposed to reduce the amount of calculation and improve computing speed. The proposed method is successfully applied in reliability evaluation for a typical low-voltage microgrid. This work is supported by National High Technology Research and Development Program of China (863 Program) (No. 2012AA050217).